Pension and Other Postretirement Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2017

Defined Contribution Plan [Abstract]

Schedule of Changes in Benefit Obligation, Plan Assets and Funded Status

The reconciliation of changes in the benefit obligation, plan assets and funded status of these plans at December 31, 2017 and 2016 is as follows:

	Pension Benefits						Other Postretirement Benefits
	at December 31,						at December 31,
	2017			2016			2017			2016
Change in benefit obligation:
Benefit obligation at beginning of period	$	735,177		$	751,617		$	700,085		$	671,755
Service cost	2,948			1,533			—			—
Interest cost	25,265			25,048			23,945			24,241
Actuarial loss (gain)	35,281			46,885			(101,379		)	77,640
Plan amendments	—			—			—			(28,164		)
Plan settlements	(29,142		)	(54,197		)	—			—
Benefits and other payments	(35,539		)	(35,709		)	(31,088		)	(45,387		)
Benefit obligation at end of period	$	733,990		$	735,177		$	591,563		$	700,085
Change in plan assets:
Fair value of plan assets at beginning of period	$	632,434		$	669,039		$	—		$	—
Actual return on plan assets	110,311			50,575			—			—
Company contributions	1,181			2,726			31,088			45,387
Benefits and other payments	(35,539		)	(35,709		)	(31,088		)	(45,387		)
Plan settlements	(29,142		)	(54,197		)	—			—
Fair value of plan assets at end of period	$	679,245		$	632,434		$	—		$	—
Funded status:
Current liabilities	$	(1,785	)	$	(2,871	)	$	(37,464	)	$	(40,611	)
Noncurrent liabilities	(52,960		)	(99,872		)	(554,099		)	(659,474		)
Net obligation recognized	$	(54,745	)	$	(102,743	)	$	(591,563	)	$	(700,085	)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss	$	243,456		$	295,152		$	301,901		$	426,392
Prior service credit	(869		)	(1,372		)	(25,759		)	(28,164		)
Net amount recognized (before tax effect)	$	242,587		$	293,780		$	276,142		$	398,228

	CWP						Workers' Compensation
	at December 31,						at December 31,
	2017			2016			2017			2016
Change in benefit obligation:
Benefit obligation at beginning of period	$	118,836		$	121,285		$	78,099		$	81,502
State administrative fees and insurance bond premiums	—			—			3,198			3,199
Service cost	5,122			4,327			5,734			7,466
Interest cost	4,050			4,283			2,321			2,499
Actuarial loss	47,939			439			3,553			121
Benefits paid	(13,107		)	(10,191		)	(14,377		)	(16,688		)
Curtailment gain	—			(1,307		)	—			—
Benefit obligation at end of period	$	162,840		$	118,836		$	78,528		$	78,099
Current assets	$	—		$	—		$	1,437		$	1,429
Current liabilities	(12,972		)	(10,763		)	(13,317		)	(13,596		)
Noncurrent liabilities	(149,868		)	(108,073		)	(66,648		)	(65,932		)
Net obligation recognized	$	(162,840	)	$	(118,836	)	$	(78,528	)	$	(78,099	)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial gain	$	(7,144	)	$	(62,714	)	$	(8,505	)	$	(12,656	)
Net amount recognized (before tax effect)	$	(7,144	)	$	(62,714	)	$	(8,505	)	$	(12,656	)

Schedule of Components of Net Periodic Benefit Costs

The components of net periodic benefit cost are as follows:

	Pension Benefits									Other Postretirement Benefits
	For the Years Ended December 31,									For the Years Ended December 31,
	2017			2016			2015			2017			2016		2015
Components of net periodic benefit cost:
Service cost	$	2,948		$	1,533		$	8,256		$	—		$	—	$	—
Interest cost	25,265			25,048			31,655			23,945			24,241		27,238
Expected return on plan assets	(42,383		)	(46,674		)	(51,528		)	—			—		—
Amortization of prior service credits	(502		)	(502		)	(579		)	(2,405		)	—		(336,327		)
Recognized net actuarial loss	8,896			9,163			20,870			23,112			19,168		102,875
Curtailment loss	—			—			5			—			—		—
Settlement loss (gain)	10,153			22,196			19,053			—			—		(8,932		)
Net periodic benefit cost (credit)	$	4,377		$	10,764		$	27,732		$	44,652		$	43,409	$	(215,146	)

The components of the net periodic cost are as follows:

	CWP									Workers’ Compensation
	For the Years Ended									For the Years Ended
	December 31,									December 31,
	2017			2016			2015			2017			2016			2015
Service cost	$	5,122		$	4,327		$	6,194		$	5,734		$	7,466		$	9,201
Interest cost	4,050			4,283			5,116			2,321			2,499			3,131
Recognized net actuarial gain	(7,631		)	(4,948		)	(5,576		)	(598		)	(395		)	(30		)
State administrative fees and insurance bond premiums	—			—			—			3,198			3,199			3,510
Curtailment gain	—			(1,307		)	—			—			—			—
Net periodic cost	$	1,541		$	2,355		$	5,734		$	10,655		$	12,769		$	15,812

Schedule of Amounts Included in Accumulated Other Comprehensive Loss to be Recognized over Next Fiscal Year

Amounts included in accumulated other comprehensive loss which are expected to be recognized in 2018 net periodic benefit costs:

				Other
	Pension			Postretirement
	Benefits			Benefits
Prior service credit recognition	$	(502	)	$	(2,405	)
Actuarial loss recognition	$	8,715		$	16,205

The following are amounts included in accumulated other comprehensive income that are expected to be recognized in 2018 net periodic benefit costs:

				Workers'
	CWP			Compensation
	Benefits			Benefits
Actuarial gain recognition	$	(854	)	$	(79	)

Schedule of Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets

The following table provides information related to pension plans with an accumulated benefit obligation in excess of plan assets:

	As of December 31,
	2017		2016
Projected benefit obligation	$	733,990	$	735,177
Accumulated benefit obligation	$	733,949	$	733,542
Fair value of plan assets	$	679,245	$	632,434

Schedule of Weighted-Average Assumptions Used

The weighted-average assumptions used to determine benefit obligations are as follows:

	Pension Benefits				Other Postretirement Benefits
	at December 31,				at December 31,
	2017		2016		2017		2016
Discount rate	3.65	%	4.31	%	3.65	%	4.22	%
Rate of compensation increase	3.73	%	3.90	%	—		—

The weighted-average assumptions used to determine net periodic benefit costs are as follows:

	Pension Benefits						Other Postretirement Benefits
	For the Years Ended						For the Years Ended
	December 31,						December 31,
	2017		2016		2015		2017		2016		2015
Discount rate	4.27	%	4.52	%	4.07	%	4.22	%	4.50	%	4.03	%
Expected long-term return on plan assets	6.90	%	7.25	%	7.75	%	—		—		—
Rate of compensation increase	3.90	%	3.80	%	3.80	%	—		—		—

The weighted-average discount rates used to determine benefit obligations and net periodic cost are as follows:

	CWP						Workers' Compensation
	For the Years Ended						For the Years Ended
	December 31,						December 31,
	2017		2016		2015		2017		2016		2015
Benefit obligations	3.75	%	4.40	%	4.60	%	3.57	%	4.05	%	4.26	%
Net periodic cost	4.40	%	4.60	%	4.21	%	4.05	%	4.26	%	3.84	%

Schedule of Health Care Cost Trend Rates

The assumed health care cost trend rates are as follows:

	At December 31,
	2017		2016
Health care cost trend rate for next year	6.06	%	6.31	%
Rate to which the cost trend is assumed to decline (ultimate trend rate)	4.50	%	4.50	%
Year that the rate reaches ultimate trend rate	2038		2038

Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates

Assumed health care cost trend rates have a significant effect on the amounts reported for the medical plans. A one-percentage point change in assumed health care cost trend rates would have the following effects:

	1 Percentage		1 Percentage
	Point Increase		Point Decrease
Effect on total of service and interest cost components	$	3,536	$	(2,962	)
Effect on accumulated postretirement benefit obligation	$	71,922	$	(60,924	)

Schedule of Fair Value of Plan Assets

The fair values of plan assets at December 31, 2017 and 2016 by asset category are as follows:

	Fair Value Measurements at December 31, 2017								Fair Value Measurements at December 31, 2016
			Quoted								Quoted
			Prices in								Prices in
			Active								Active
			Markets for		Significant		Significant				Markets for		Significant		Significant
			Identical		Observable		Unobservable				Identical		Observable		Unobservable
			Assets		Inputs		Inputs				Assets		Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)		Total		(Level 1)		(Level 2)		(Level 3)
Asset Category
Cash/Accrued Income	$	5,202	$	5,202	$	—	$	—	$	639	$	639	$	—	$	—
US Equities (a)	12		12		—		—		11		11		—		—
Mercer Common Collective Trusts (b)	674,031		—		—		—		631,784		—		—		—
Total	$	679,245	$	5,214	$	—	$	—	$	632,434	$	650	$	—	$	—

__________

(a) This category includes investments in US common stocks and corporate debt.

(b) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy but are included in the total.

Schedule of Expected Benefit Payments

The following benefit payments, reflecting expected future service, are expected to be paid:

			Other
	Pension		Postretirement
	Benefits		Benefits
2018	$	44,778	$	37,464
2019	$	44,035	$	37,163
2020	$	43,117	$	37,071
2021	$	42,124	$	36,862
2022	$	42,644	$	36,228
Year 2023-2027	$	206,682	$	172,756

The following benefit payments, which reflect expected future claims as appropriate, are expected to be paid:

			Workers' Compensation
	CWP		Total		Actuarial		Other
	Benefits		Benefits		Benefits		Benefits
2018	$	12,972	$	14,390	$	11,880	$	2,510
2019	$	10,065	$	14,120	$	11,547	$	2,573
2020	$	8,841	$	14,110	$	11,473	$	2,637
2021	$	8,203	$	14,035	$	11,332	$	2,703
2022	$	8,024	$	14,146	$	11,375	$	2,771
Year 2023-2027	$	42,525	$	53,187	$	38,259	$	14,928